ON THE EVOLUTION OF SUPERCONDUCTIVITY IN LA1.5-XBA1.5-XCA2XCU3O7-DELTA (0.0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1.0)

Simultaneous replacement of La and Ba by Ca in La1.5Ba1.5Cu3O7+delta (336 phase) was attempted to explore the possible transformation of non-superconducting 336-phase into the superconducting 1113-phase (CaBaLaCu307-delta) and thereby investigating the evolution of superconductivity as a function of ''x'' in La1.5-xBa1.5-xCa2xCu3O7-delta (0.0 less-than-or-equal-to x less-than-or-equal-to 1.0). In this system, single pbase compounds result only for x less-than-or-equal-to 0.3 and nearly phase pure compounds result for x values in the range 0.3 less-than-or-equal-to x less-than-or-equal-to 0.6, whereas samples with x>0.6 contain a substantial amount of impurity phases. All samples with 0.2 less-than-or-equal-to x less-than-or-equal-to 1.0 were found to be superconducting with T(c) values in the range 57-72 K. On the other hand, partial replacement ofeither La or Ba by an equivalent amount of Ca in La1.5Ba1.5Cu3O7+delta resulted in a different T(c)-behaviour, viz. the sample with nominal composition La1.5(Ba1.0CaO.5)Cu3O7+delta exhibiting a T(c)(R=0) value of 45 K, whereas the one with composition (La1.0Ca0.5)Ba1.5Cu307-delta exhibiting a higher 7, value of 72 K. The present studies suggest that the actual cationic composition for the high-T(c) superconducting phase in the Ca-Ba-La-Cu-O system need not be in the 1:1:1:3 ratio.